1. Field of the Invention
The present invention relates generally to an emission control system/after treatment system for an engine and, in particular, to a passive mid bed air injection apparatus for an engine.
2. Discussion of the Prior Art
Natural gas engines are utilized in a number of different environments, including gas compression applications, power generation applications, oil field power generation applications, etc. Natural gas engines can be provided with a catalytic converter that converts pollutants/emissions from an exhaust stream of the engine into less toxic pollutants. In the past, engine exhaust was manipulated to be slightly richer (e.g., greater amount of fuel such that ratio of air to fuel is below stoichiometry) to improve reduction of pollutants from the exhaust stream such as unburned or partially burned hydrocarbons (HC), nitrogen oxides (NOx), etc.
As a consequence of the engine exhaust being slightly richer, a larger amount of other pollutants, such as ammonia (NH3), carbon monoxide (CO), etc., were present in the exhaust stream. Accordingly, there is a need, and it would be beneficial, to efficiently remove pollutants (e.g., ammonia (NH3) and carbon monoxide (CO)) from the exhaust stream by increasing the amount of air in the catalytic converter without the use of active controls such that a ratio of air to fuel is above stoichiometry.